(1) Field of the Invention
This invention relates to a mechanism for varying the timing of the valves of an internal combustion engine, and more particularly relates to a mechanism for varying the time at which the valves of an internal combustion engine open and close, the period during which the valves are open, and the maximum lift thereof in order to optimize the efficiency of the engine under different operating load and speed conditions.
(2) Description of the Prior Art
Various types of mechanisms and devices have been heretofore advanced for varying the timing of the intake and/or exhaust valves of internal combustion engines in order to improve the efficiency and performance of the engine when operating under different speed and load conditions. One such mechanism is disclosed and claimed in my prior U.S. Pat No. 4,205,634, granted June 3, 1980. This mechanism includes a rotatable camshaft having a plurality of conjugate or multi-element cam assemblies thereon, there being one assembly for at least each intake valve of the engine. Each conjugate cam assembly includes an identical pair of axially spaced cams and a smaller and differently contoured cam positioned between the two axially spaced cams. The axially spaced cams are contoured to provide a timing for the associated valve such as will optimize the performance of the engine throughout one operating load and speed range or condition, and the smaller cam is contoured to provide a different timing for the valve such as will optimize the performance of the engine throughout another operating load and speed range or condition.
The mechanism disclosed in U.S. Pat. No. 4,205,634 includes an elongated finger follower positioned between each axially spaced pair of cams and shiftable to a retracted position wherein the follower is out of contact with the central cam for all rotated positions thereof. Consequently, the timing of each valve is controlled solely by the axially spaced pair of cams.
Each finger is also shiftable to an extended position wherein the finger engages the central cam of its assembly throughout at least a portion of or for a complete revolution of the cam assembly. Consequently, the timing of the valve is controlled either by the axially spaced cams, or in part by the axially spaced pair of cams and the central cam, or solely by the central cam. Different valve timings may thus be obtained for optimizing the power and efficiency of the engine for different speed and load conditions by extending or retracting each of the elongated fingers of the mechanism.
In my prior U.S. Pat. No. 4,382,428 granted May 10, 1983, another variable valve timing mechanism is disclosed and claimed which improves upon the mechanism disclosed in my prior U.S. Pat. No. 4,205,634. The mechanism disclosed in my pending patent application employs a single cam for controlling the operation of one of the valves of the engine and an elongated finger follower disposed between the cam and the linkage for effecting movement of the associated valve. Each finger follower has nonplanar control surfaces respectively engaging the cam and linkage means associated therewith, and operating means connected to the proximal end of the finger for shifting the latter relative to the cam member and linkage means in order to vary the timing, duration of the open period, and maximum lift of the valve. The nonplanar or control surfaces on each finger include contiguous portions of decreasing and increasing radius. The aforementioned operating means includes a rotatable shaft and a plurality of cranks interconnecting the shaft and the proximal ends of the respective contoured finger followers. Consequently, each crank is effective to shift the proximal end of the finger associated therewith in an arcuate path and throughout a range of positions such as to cause different portions of the concave control surface of the finger to move into engagement with the cam in accordance with the changing load and speed conditions of the engine.
In addition to the variable valve timing mechanisms disclosed in my prior patent and pending U.S. patent application, a variable valve timing mechanism is disclosed in the Roan U.S. Pat. No. 2,266,077 for varying the timing of the intake and exhaust valves of an internal combustion engine. The mechanism disclosed in the Roan patent employs an arm or yoke for each of the valves of the associated engine, the distal end of the arm being movable between different positions with respect to the cam and a tappet associated with the valve in order to change the timing of the valve. Cam engaging shoes on the distal ends of the arms coact with the cams and their associated tappets to effect changes in the time at which the valve opens and closes, and the period that it remains open, thereby to improve the operating efficiency and performance of the engine for different speed and load conditions. Instead of shoes, the distal or operating ends of the yokes of the Roan variable valve timing mechanism may include one or more tappet rollers for this purpose.
An engine valve control mechanism is also disclosed in the Gregory U.S. Pat. No. 2,410,411, wherein rollers are provided on the cam engaging ends of the rocker arms for the intake and exhaust valves of the engine and wherein variation of the timing of the valves is achieved by lateral shifting of the rocker arms relative to the ends of the valves.
A variable valve control mechanism is also disclosed in the Oldberg U.S. Pat. No. 4,261,307, wherein two angularly arranged pads on an auxiliary rocker arm engage an associated intake valve, the rocker arm being pivotally supported on a shaft adjacent to rhe intake valves of the engine. The shaft upon which the rocker arm for each intake valve is mounted is longitudinally shiftable in a slot in a control arm. Consequently, movement of the shaft on which the auxiliary rocker arms are mounted changes the angular position of the pads of the rocker arm and the position of one of the pads with respect to the cam and cam follower. This changes the time at which the valve closes. The variable valve timing control arrangement disclosed in the Oldberg patent depends upon sequential engagement of two pads with the valve actuating cam to change the timing. In a simplified arrangement, Oldberg employs a single roller between the intake valve cam and its follower to vary the closing time of the valve.